hw/char/sh_serial: Do not abort on invalid access

hw/char/sh_serial: Do not abort on invalid access

Replace fprintf with qemu_log_mask LOG_GUEST_ERROR as the intention is
to handle valid accesses in these functions so if we get to these
errors then it's an invalid access. Do not abort as that would allow
the guest to crash QEMU and the practice in other devices is to not do
that just log and ignore the invalid access. While at it also simplify
the complex bit ops to check if a return value was set which can be
done much simpler and clearer.

Signed-off-by: BALATON Zoltan <balaton@eik.bme.hu>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <6b46045141d6d9cc32e17c223896fa1116384796.1635541329.git.balaton@eik.bme.hu>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>